1. Field of the Invention
The present invention relates to a liquid applying apparatus and an ink jet printing apparatus, and specifically, to a liquid applying apparatus that applies a liquid to a medium for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials. Likewise, the present invention relates to an ink jet printing apparatus comprising a mechanism that applies the liquid to a print medium used for ink jet printing, for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials.
2. Description of the Related Art
A spin coater, a roll coater, a bar coater, and a die coater are known as systems for applying a liquid or an aqueous material to various media. These applying systems are premised on continuous applying on relatively long applying media. Thus, for example, if applying media having a relatively small size and intermittently conveyed are to be applied the liquid to, paint beads may be disturbed at a position at which applying is started or ended. In this case, the coats obtained may be non-uniform among the applying media.
A known configuration that can solve this problem is described in Japanese Patent Application Laid-open No. 2001-070858. On the basis of the die coater system, this configuration uses a rotating rod bar and ejects a paint to the rod bar through an ejection slit to form a coat on the rod bar. The coat formed is contacted with and transferred to an applying medium as the rod bar rotates. In this case, when the coat formed on the rod bar is not transferred or applied to the applying medium, the paint is returned to a head by the rotation of the rod bar. The paint is then collected via a collecting slit. In other words, the rod bar continues to rotate even during non-applying, while the paint is being formed into a coat on the rod bar. This enables a uniform coat to be obtained even if applying media are intermittently supplied and applied the paint.
Even in the field of ink jet printing apparatuses, those using a liquid applying mechanism are known. Japanese Patent Application Laid-open No. 2002-517341 describes an apparatus which uses a doctor blade contacting with a roller and in which the application liquid is collected between the blade and the roller so that the application liquid is applied to the roller as the roller rotates. As the roller rotates, the application liquid applied to the roller is transferred and applied to a support conveyed between this roller and another roller. Japanese Patent Application Laid-open No. 08-072227 (1996) similarly discloses a mechanism in an ink jet printing apparatus which applies a treatment liquid before printing which liquid insolubilizes dyes. In Embodiment 1 of this document, the treatment liquid in a replenishing tank is pumped by being attached to the rotating roller. At the same time, the treatment liquid pumped is applied to print paper.
With the configurations described in the above patent documents, an application liquid is applied or supplied to the surface of the rod bar or roller. However, the part of the rod bar or roller to which the application liquid is applied or supplied is open to or in communication with the air. Thus, disadvantageously, the application liquid may be evaporated or for example, the application liquid may leak when the posture of the apparatus is changed.
In particular, with an ink jet printing apparatus such as a printer, in view of, for example, the leakage of the liquid caused by a change in the posture of the apparatus, it is difficult to apply the applying mechanism described in the above documents to the apparatus if its size has been reduced.
In contrast, Japanese Patent Application Laid-open No. 08-058069 (1996) discloses a configuration that seals a part that applies or supplies inks, that is, application liquids, to a roller. The applying mechanism described in this document operates in a gravure printing apparatus to apply inks to a roller (applying roller) having the surface of which is formed with a pattern of a printing plate. This mechanism uses an ink chamber having two doctor blades arranged at two vertical positions along a peripheral surface of the roller and extending in a longitudinal direction of the roller and elastic members provided at the opposite sides of the two doctor blades. The chamber is contacted with the peripheral surface of the roller to form a liquid chamber between the ink chamber and the roller. Then, the roller is rotated to apply or supply the application liquid from the liquid chamber to the roller.
However, the sealing arrangement disclosed in Japanese Patent Application Laid-open No. 08-058069 (1996) may provide an insufficient sealing property. That is, the doctor blades are separate from the elastic members provided at the opposite ends of each of the doctor blades through both doctor blades and elastic members are abutted against the roller for sealing. Thus, for example, the pressure exerted on the roller upon abutment may vary significantly between these members. In this case, the abutting pressure differs markedly between the junctions between the doctor blades and the elastic members and the other parts. Thus, the sealing may be insufficient in parts with a lower abutting pressure, resulting in the leakage of the liquid. If the abutting pressure itself is set at a large value in order to prevent the leakage of the liquid caused by the non-uniform abutting pressure, the application of inks to the roller may be unsatisfactory, which application is carried out by the blades and the roller in cooperation.
Moreover, in Japanese Patent Application Laid-open No. 08-058069 (1996), the ink chamber comprising the doctor blades and the elastic members is moved by engaging the ink chamber with a shaft in which a thread groove is formed and then rotating the shaft. The abutting pressure between the roller and the doctor blades and elastic members is exerted by simply fixing the position of the chamber. Thus, for example, if there are small concaves and convexes on the peripheral surface of the roller, the abutment does not conform to the concaves and convexes. This may degrade the sealing property to prevent inks from being favorably applied to the roller.
Further, Japanese Patent Application Laid-open No. 08-058069 (1996) describes the doctor blades provided to scrape extra inks adhering to the surface of the roller. Accordingly, this document does not disclose the configuration of blades or abutting portions which are preferred in association with the sealing property if the liquid is applied to the entire surface of a medium such as paper which has a certain thickness.
As described above, in association with the supply of the coating liquid to the roller, an arrangement is important which uses the abutting portion to appropriately seal the coating liquid chamber formed between the abutting portion and the roller. More specially, it is extremely important to provide the liquid holding space with a good sealing condition in order to keep a good quality of the applying liquid and enhance a handling ability of the applying apparatus in moving and transporting it. Accordingly, it is required to prevent the applying liquid from being evaporated and/or leaked while a roller remains stopped for a long time and when the posture of the applying apparatus happens to be tilted.